Desulfurization of phenols



United States Patent DESULFURIZATION OF PHENOLS N0 Drawing. Application February 4, 1954, Serial No. 408,301

Claims. (Cl. 260-627) This invention relates to the purification of phenols. More particularly, it relates to the desulfurization of alkyl phenols derived from aqueous alkaline extracts of hydrocarbon materials such as petroleum oils, especially cracked distillates.

The extraction of phenolic materials from petroleum oils and coal tar distillates by treatment with strong aqueous caustic alkali, such as 25 to 45 Baum sodium or other alkali metal hydroxide, to produce an aqueous alkali metal phenolate solution, is well known in the art. The phenolic material is generally recovered from the aqueous alkali metal phenolate solution by first neutralizing and/or acidifying the alkali metal phenolate in order to spring the phenols, whereby an aqueous layer and a phenol layer are formed, and separating the phenol layer. The recovered phenols are usually subjected to distillation to effect fractionation thereof. The phenols thus obtained are frequently termed in .the art acid oils or cresylic acids.

The phenols obtained by the above-described procedures are generally contaminated by organic sulfur compounds, particularly mercaptans, which decrease. their usefulness. It is known that phenols can be desulfurized to a certain extent by treatment with free sulfur at elevated temperatures of the order of 60-200 C. for an extended period of time, usually 2 to hours. The thus purified phenols are subsequently subjected to distillation to effect fractionation thereof. The known desulfurization method requires a long period of time for effective desulfurization. In addition to increasing the process time for recovery of the phenolic material, the known method requires an additional step which further complicates the recovery process.

It has now been found that crude phenols can be eifectively desulfurized during the distillation step simultaneously with the fractionation thereof, by carrying out the distillation in the presence of free sulfur and an alkaline material, such as an alkali metal hydroxide. By this method, phenols, particularly alkyl phenols, can be effectively desulfurized without the increase in process time and the additional step which are required by the known method.

The invention is of particular utility for the desulfurization of alkyl phenols boiling below about 240 C. which are obtained by the extraction of thermally and catalytically cracked distillate fractions having a boiling range of from about 100 C. to about 250 0., followed by acidification of the alkaline extract, preferably with carbon dioxide, in order to spring the alkyl phenols. The sprung alkyl phenols can be recovered from the acidified extract by various methods. For example, the acidified extract can be permitted to settle to obtain an aqueous phase and an alkyl phenol phase, the resulting phases separated, and the separated alkyl phenols washed with water to remove alkali metal salts and T en dehydrated. The recovered alkyl phenols can then be desulfurized while effecting the fractionation thereof by distillation in the presence of free sulfur and an alkaline material in accordance with the present invention.

By reason of the free sulfur being present during distillation, an oxidizing environment is maintained in the distillation zone whereby disulfides are formed from mercaptans and reduction of disulfides to mercaptans is prevented. The disulfides are high boiling and, therefore, do not appear in the top product from the distillation zone. The presence of at least a trace of an alkaline material, such as an alkali metal hydroxide, more effectively prevents the appearance of mercaptans in the phenol product.

The term free sulfur is used herein to include sulfuryielding compounds, such as inorganic polysulfides, especially alkali metal polysulfides, which liberate elemental sulfur under the conditions of treatment, as well as elemental sulfur.

The amount of free sulfur employed in the process will depend upon the mercaptan content of the phenolic material to be treated. The amount employed should be suflicient to maintain an oxidizing atmosphere in the distillation zone. Generally, an amount of from about 0.05% to about 5% by weight, based on the phenolic material to be treated, will be found to be satisfactory.

The alkaline material employed in the present process is preferably an alkali metal hydroxide, such as sodium hydroxide. Only a trace of alkaline material need be present for effective results. The alkaline material can be associated with the free sulfur as an incidental impurity. For example, an alkali metal sulfide solution when exposed to air develops alkalinity from oxidation, and the resulting partially oxidized or old alkali metal sulfide, upon conversion to the corresponding polysulfide, can be effectively employed in the process of the invention. Generally, an amount of from about 0.005% to about 1% by weight, based on the alkyl phenols to be treated, will be satisfactory. The amount of alkaline material employed should be insufiicient to convert substantial amounts of the phenols to the corresponding phenolates.

The free sulfur and the alkaline material can be added to the distillation zone in solid form. For example, a cast stick of sulfur and a shaving device for adding the sulfur at a low and constant rate can be used. It is generally preferred to add the reagents to the distillation zone in solution, preferably via a slip stream of reflux. Addition in the form of an aqueous solution of an alkali metal hydroxide and an alkali metal polysulfide is usually most convenient. A suitable sulfur-sodium hydroxide solution can be prepared, for example, by heating 16 parts by weight of sodium sulfide nonahydrate, 6 parts by weight of elemental sulfur, 0.1 part by weight of sodium hydroxide, and 3 parts by weight of water very slowly to the temperature at which a homogeneous solution is obtained.

Normally, the rate of mercaptan formation from disulfides increases with an increase in the distillation temperature. Therefore, it is advisable to carry out the distillation of the phenolic material rapidly and at a low temperature. Preferably, the distillation is carried out under a pressure of not greater than about 50 mm. Hg.

The phenolic fractions obtained by the present process, particularly the lower boiling fractions, generally contain minor amounts of hydrogen sulfide which is formed during the oxidation of mercaptans to disulfides. The

sulfur and sodium hydroxide were added to the distillation zone in the form of a solution of sodium polysulfide and sodium hydroxide and via a slip stream of reflux. The distillation was carried out under a pressure of 11 mm. Hg, and the reflux ratio was 1:1. 'For purposes of comparison, crude alkyl phenols were subjected to distillation in the absenceof any added agents, and crude'alkyl phenols were subjected to distillation after refluxing with 1% by weight, based on the charge, of sulfur and 3% by weight, based on the charge, of sodium sulfide nonahydrate for a period of one hour at a temperature of 250 F. The results of the various tests are given in the table.

Mercaptan Sulfur, percent w.

Distillation Temperature, 11 mm. Hg,

1 The sultil'r was normally added constantly at a rate which resulted in the net addition of 1% w., basis charge, at the end of the distillaton.

1 The sodium su1fide used was a mixture of fresh sodium sulfide and oldisodiurn sulfide. Old droxide as a contaminant.

3 The alkyl phenols were refluxed for 1 hour at 250 F. in the presence of 1% w. sulfur and 3% w. sodium sulfide nonahydrate.

From the results in the above table, it is readily apparent that alkyl phenols of substantially reduced mercaptancontent can be obtained by the process of the present invention which requires no increase in process time. Furthermore, superior results were obtained by the present-process than by prior refluxing with sulfur for one hour' at 250 F.

1 claim as my invention:

1. In a method for the recovery of alkyl phenols from sodium sulfide contained sodium hyan alkaline extract of a cracked petroleum distillate wherein said alkaline extract is acidified to spring alkyl phenols, the sprung alkyl phenols are recovered from the acidified extract, the recovered alkyl phenols containing substantial amounts of mercaptans, and the recovered alkyl phenols are subjected to distillation, the improvement which comprises carrying out said distillation rapidly at low temperature under a pressure below atmosp'he'r'ic in the presence of an amount of free sulfur sufficient to maihtain an oxidizing atmosphere in the distillation zone and a minor amount of an alkali metal hydroxide, whereby the aromatic mercaptan content of the alkyl phenols is substantially reduced.

2. A method of desulfurizing mercaptan-containing alkyl phenols which comprises subjecting said alkyl phenols to distillation rapidly at low temperature under a pressure below atmospheric in the presence of free sulfur and'an alkali metal hydroxide.

3. A method of 'desulfurizing mercaptan-containing alkyl phenols which comprises subjecting said alkyl phenols to distillation rapidly at low temperature under a pressure below atmospheric in the presence of an aque: ous solution of an alkali metal polys'ulfide and an alkali metal hydroxide.

4. A method of desulfurizing mercaptan-containing phenols which comprises subjecting said phenols to distillatio'n rapidly at low temperature under a pressure below atmospheric in the presence of free sulfur and an alkali metal hydroxide.

5. A method of desulfurizing mercaptan-containing alk yl' phenols which comprises subjecting said alkyl phenols to distillation rapidly at low temperature under a pressure not greater than about mm. Hg in the presence of free sulfur and an alkali metal hydroxide, the weight of said free sulfur amounting to from about 0.05% to about 5.0% of the weight of said alkyl phenols and the weight of said alkali metal hydroxide amounting to from about 0.005% to about 1.0% of the Weight of said alkyl phenols.

References Cited in the file of this patent UNITED STATES PATENTS 1,926,665 Banta Sept. 12, 1933 1,982,120 Oosterhout Nov. 27, 1934 2,163,227 Hufid et al. June 20, 1939 2,218,139 Thomas et al Oct. 15, 1940 2,279,711 Luten et al Apr. 14, 1942 2,288,281 Huijser et al June 30, 1942 

1. IN A METHOR FOR THE RECOVERY OF ALKYL PHENOLS FROM AN ALKALINE EXTRACT OF A CRACKED PETROLEUM DISTILLATE WHEREIN SAID ALKALINE EXTRACT IS ACIDIFIED TO SPRING ALKYL PHENOLS, THE SPRUNG ALKYL PHENOLS ARE RECOVERED FROM THE ACIDIFIED EXTRACT, THE RECOVERED ALKYL PHENOLS CONTAINING SUBSTANTIAL AMOUNTS OF MERCAPTANS, AND THE RECOVERED ALKYL PHENOLS ARE SUBJECTED TO DISTILLATION, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT SAID DISTILLATION RAPIDLY AT LOW TEMPERATURE UNDER A PRESSURE BELOW ATMOSPHERIC IN THE PRESENCE OF AN AMOUNT OF FREE SULFUR SUFFICIENT TO MAINTAIN AN OXIDIZING ATMOSPHERE IN THE DISTILLATION ZONE AND A MINOR AMOUNT OF AN ALKALI METAL HYDROXIDE, WHEREBY THE AROMATIC MERCAPTAN CONTENT OF THE ALKYL PHENOLS IS SUBSTANTIALLY REDUCED. 